The present invention relates to a proton conductor film, manufacturing method thereof, a fuel cell provided with the proton conductor film, and manufacturing method thereof.
As a high molecular solid electrolyte type fuel cell for automobile driving, there has recently been known such a cell employing a proton (hydrogen ion) conducting high molecular or polymer material, such as perfluorosulfonic acid resin, e.g., a product manufactured by DuPont under the trade name of Nafion®.
Among newer types of the known proton conductors, there are polymolybdenic acids or oxides having a large quantity of hydrated water, such as H3Mo12PO40.29H2O or Sb2O5.5.4H2O.
When placed in a wetted state, the above-mentioned polymer materials or hydrated compounds exhibit high protonic conductivity at or near the ambient temperature.
Taking an example of the perfluorosulfonic acid resin, protons desorbed from its sulfonic acid groups by electrical dissociation are bonded with the moisture taken in large quantities into the polymer matrix by hydrogen linkage to yield protonated water, that is oxonium ions (H3O+). The protons then are able to migrate smoothly in the polymer matrix in the form of oxonium ions. Thus, the matrix material of this type exhibits a rather high proton conduction effect even at an ambient temperature. Recently, a proton conductor having a conduction mechanism entirely different from that of the above compounds has recently been developed.
In this regard, a composite metal oxide of a perovskite structure, such as SrCeO3, doped with Yb, has been found to exhibit protonic conductivity, without using the moisture as a movement medium. In this composite metal oxide, it is premeditated that the protons are conducted by channeling, by themselves, through oxygen ions forming the skeleton of the perovskite structure.
These conductive protons are not present from the outset in the composite metal oxide. It may be premeditated that, when this perovskite structure contacts with steam contained in the ambient atmospheric gas, water molecules thereof at a higher temperature react with defective oxygen formed in the perovskite structure on doping to yield protons for the first time by this reaction.
With the above-described various proton conductors, a number of problems exist.
In this regard, a matrix material, such as perfluorosulfonic acid resin, must be continuously placed in a sufficiently wetted state, during use, in order to maintain a high proton conductivity. For example, the conventional proton conductor has a deficiency that its atmosphere dependency is high, such that moisture or steam needs to be supplied, and moreover the operating temperature is excessively high or of a narrow range.
In a system structure of for example a fuel cell, a humidifier or other various ancillary devices are required, thus possibly leading to an increased scale of the system and to increased cost in constructing the system. Moreover, the operating temperature range is not that wide in order to prevent freezing or boiling of the moisture contained in the matrix.
In addition, in the case of the aforementioned composite metal oxide, having the perovskite structure, the operating temperature needs to be maintained at as high as 500° C. or higher in order to achieve meaningful proton conduction.
A need therefore exists to provide improved proton conductors, fuel cells and methods of manufacturing same.